Method of gas plating light metals



March 31, 1959 F. E; DRUMMOND ,1

METHOD OF GAS PLATING LIGHT METALS Filed July 15, 1955 I substratum IChemical or Mechanical Surface Cleaning Flgl Chemically Clean.Substratum /Under Partial Vacuum or lnert Atmosphere Heat SubstrotumAbove the Decomposition Temperature at Al or Mg Plating Gas Heatedsubstratum Contaoteo' with Al Mg Plating Gas whereby Light Metal isDeposited thereon L l v Coo/in:

Light Metal Plated 5 uh s t rat u'm F Al orMg Plating m 1 Substratum(metal, glass, etc. material) IN V EN TOR.

I F OLSOM E. DRUM/MONO BY Attorneys United States Patent METHOD OF GASPLATING LIGHT METALS Folsom E. Drummond, Washington, D.C., assignor toThe Commonwealth Engineering Company of Ohio, Dayton, Ohio, acorporation of Ohio Application July 13, 1955, Serial No. 521,921

2 Claims. (Cl. 117-50) This invention relates to gas plating of lightmetal such as aluminum, magnesium or the like, and to composite metalbodies produced thereby.

Attempts to produce coatings of light metals such as aluminum andmagnesium have been difficult and of little value commercially becauseof the necessity of volatilizing the metals. Aluminum metal vaporizes ata temperature of 1800 C. (3272 F.) and magnesium at 1110 C. (2030 F.).The high temperature requirements for volatilizing these light metals,together with the difliculty of handling such hot metal vapor, hasmitigated against their use in conventional plating processes.

In accordance with the present invention heat decomposable compounds ofthe light metals are utilized to deposit the pure metal by gaseousdeposition. The process overcomes the difiiculties of working with ultrahigh temperature gases as when using volatilized metals.

In accordance with the present invention, aluminum or magnesium metal,or suitable mixtures thereof are deposited directly upon a substratumsuch as steel, iron,

copper, magnesium, aluminum or alloy metals to provide a tenaciouslybonded metal layer or coating oflight metal. The process permits gasplating of light metals at relatively low temperatures, as compared tothat of the volatilized metals, and wherein the light metal is depositeddirectly on the substratum without the need of utilizing an intermediatebonding layer.

The principal object of the present invention is to gas plate such lightmetals as aluminum or magnesium directly onto a supporting or basesurface which may comprise a ferrous or non-ferrous metal or suitablealloy metal whereby the base surface portion is provided with an outershell of substantially pure aluminum or magnesium metal as desired.

Another object of the invention is to provide a composite metal articleconsisting of a substratum of light metal, e.g. magnesium, which isprotected by an outer coating or layer of aluminum metal depositedthereon by gas plating.

Another object of the invention is to provide a composite metal articleand made of either light or heavy metals as described, which comprises agas plated layer of aluminum metal or magnesium metal.

Another object of the invention is to provide a method whereby lightmetal, such as magnesium and aluminum.

may be plated onto metal castings, sheets, strips or the like andfabricated into a wide variety of products and shapes, and where it isdesirous that the article have an outer portion composed of light metal.

Another object of the invention is to provide a method 5 whereby metalssuch as steel, iron, copper and the like may be suitably protected witha layer of aluminum.

metal, the same being depositeddirectly onto the sub- I stratum.

a supporting base metal without the necessity of em 2,880,115 PatentedMar. 31, 1959 "ice 2 ploying an intermediate bonding layer or alloy ashas been the practice heretofore.

Another object of the invention is to provide an improved method ofgaseous metal plating the light metals of groups II and III of theperiodic system onto the surface of articles. 1

Another object of this inventionis to provide an improved process forplating light metals such as aluminum and/or magnesium, or other lightmetals of groups II and III in the periodic system, and whereinorgano-metal compounds of these light metals are utilized which areheat-decomposable at relatively low temperatures, as compared with thevaporized metal, and whereby deposition of these light metals in theform of a thin film or plate is accomplished under conditions which arecommercially practical. It is still another object of the invention toprovide a method for producing aluminum coated articles whereby aluminummetal is deposited onto the surface of the substratum and into the poresand interstices of the surface to provide an interlocked substantiallyintegral layer or coating of aluminum metal thereon.

These and other objects and advantages will become apparent as thedescription proceeds.

In accordance with the present invention, metal surfaces such asmagnesium, aluminum, steel, iron, copper and the like, and alloy metalsare cleaned to remove foreign matter and then subjected to gas platingutilizing a suitable heat-decomposable organo-metallic compound ofaluminum or magnesium, or suitable mixtures there-. of, to provide afinished composite metal product. The process may be carried out usingan inert atmosphere such as helium, argon, or nitrogen or the operationmay be carried out in a vacuum.

The present invention comprises subjecting a clean metal surface to gasplating utilizing suitable organometallic compounds of aluminum ormagnesium, and wherein the light metal compounds employed areheatdecomposable at temperatures substantially below the vaporizationpoint of the light metals and decomposition or disassociation of thecompound takes place in an atmosphere which is inert and free of oxygento bring about deposition of the light metal without encounteringoxidation reactions.

In carrying out the gaseous metal plating in accordance with thisinvention, in the production of light metal plated productsorgano-metallic compounds of aluminum, magnesium, etc., in either liquidor gaseous state, are preferably admixed with dry inert gas such ashelium, argon, nitrogen, etc., and brought in contact with the heatedpreviously cleaned metal surface upon which the light metal is to beplated, the temperature of the metal on which the plating is to bedeposited is high enough to bring about decomposition or disassociationof the light metal organo-metallic compound and deposition of the metalconstituent onto the metal substratum.

Cleaning of the" metal surface to be plated may be efiected by employingmechanical or chemical means, or suitable combinations thereof.Sandblasting, wire brushing, or the like, may be used to remove solidforeign particles.- Where the metal surface is to be degreased andcleaned, the same may bewashed with petroleum solvents such as xylol,toluene, or the like, and use may be made of aqueous all'taline washes.A suitable treatment consists of immersing the-metal article in asolution containing 10% sodium hydroxide, the temperature of thesolution being approximately C. and allowing the metal to soak thereonfor from ten to thirty minutes. Thereafter the article is removed,thoroughly rinsed with clean water and dried at a temperature around 300C for a suflicient time to remove all moisq ture and provide athoroughly dry chemically clean metal surface for gas plating with lightmetal compounds. The thus cleaned metal surface which is retained out ofcontact with air, and preferably in an inert atmosphere such asnitrogenor helium, issubjected to gaseous metal plating by bringing thesame while heated in contact with a heat-decomposable organo-metalliccompound. 'Following the gaseous metal plating the metal may 'again beheatedif desired to stabilize the coating, as for'e'xample heatannealing the same bysubjecting to a heat of approximately 250 300 C.for from'one to two hours. This annealing step, however, may beomitted'where the sameis not required, or the does not necessitate .it.

The'. accompanying drawing illustrates a preferred method of carryingout thei'proce'ss and the'a'rticle 'pro duced thereby.

Figure 2 illustrates a sectional view taken'through ,a substratum platedwith light metal by decomposition of a gaseous metal compound ofaluminum or magnesium, in accordance with this invention. 7

The following organo-metallic compounds of aluminum and magnesium areuseful in gas plating these light metals in accordance with thisinvention. Such compounds which are suitable may have the generalformula: Me(R),,, wherein Me represents aluminum or magnesium, n the.valency of the metal, and R. is. hydrogen, or a hydrocarbon radical.Typical examples of suchjaluminum and magnesium compounds are listed asfollows ALUMINUM- Alkyl and aryl compounds Al(C,,l-l 1) and aromaticderivatives Aluminum trimethyl Aluminum triethyl Aluminum triphenylsAluminum benzyl lithium Hydrides Aluminum tri-hydride Aluminum dimethylhydride Aluminum diethyl hydride Aluminum bore-hydride Nitride: andbenzoates Aluminum nitride Aluminum nitro-benzoate Esters Figure l is aflow sheet illustrating the'process', and I use of the' article mustplated I In accordance with the process of the present invention, gasplating of these light metals on various substrata may be carried oututilizing volatile or gaseous compounds of aluminum or magnesium whichare heatdecomposable. Metallic compounds of aluminum or magnesium, suchas listed above, and which may be in a solid or liquid state andvolatilized to a gaseous state are used. The gaseous compound of themetal is brought in contact with the surface which is to be plated withthe light metal and caused to decompose or disassociate and deposit thelight metal constituent onto the surface.

The process of the invention thus differs from other suggested coatingmethods wherein special electrolytic baths are required and highor lowvoltage power means are employed. Further, while it is known that metalhalides, particularly the chloride of aluminum, may be reacted withhydrogen to produce aluminum and hydrochloric acid, it has not beenknown to plate out aluminum, magnesium and such light metals byemploying heat-decomposable gaseous compounds of these metals, the samebeing brought in contact with the article to be plated under controlledtemperature and atmospheric conditions to cause decomposition ordisassociation of the gaseous metal compound and deposition of the metalconstituent onto the surface of the article.

The following examples are illustrative of the method of gas platingthese light metals but it is understood that I the examples are notlimitative of this invention.

EXAMPLE I Magnesium metal casting sandblasted to provide a I cleansurface is heated to about 350 C.400 C. in an atmosphere of dry heliumcontaining magnesium diphenyl. This magnesium organo-metallic compounddecomposes at about 280? C. disassociating into magnesium and diphenyl.The process is carried out under atmos- 280 C. MEN-R I): (CaHl):

Dry N! EXAMPLE II In this instance magnesium casting which is freed offoreign matter is heated to 300-400 C. and contacted with an atmosphereof dry helium containing aluminum trimethyl, and employing vacuumpressure conditions e.g. 15-20 mercury. Aluminum trimethyl starts todisassociate at about 250 C. whereupon the aluminum metal is depositedonto the surface of magnesium.

EXAMPLE III Magnesium sheet metal is gas plated with magnesium metalsimilarly as in Example I, but under sub-atmospheric pressure conditionsof from 18-25 mercury, and using dry nitrogen as the inert gas carrierfor magnesium diphenyl.

EXAMPLE IV In this instance steel strip material previously freed offoreign matter is heated to 350 C. and contacted with an atmosphere ofdry helium containing magnesium diethyl, and under sub-atmosphericpressure conditions as in Example III. Upon decomposition of themagnesium alkyl compound magnesium is deposited onto the surface of thesteel.

EXAMPLE V Iron castings are gas plated with magnesium as in Example IVemploying methylmagnesium iodide which thermally decomposes at about 250C.

EXAMPLE VI Magnesium metal is gas plated on steel as in Example IV usingtriarylmethylmagnesium iodide and at plating temperatures to bring aboutthermal decomposition of the iodide in an atmosphere of dry inert gas,e.g., nitrogen.

. .EX B YQW In this instance a 50-50 weight mixtureof aluminum triethyland magnesium diethyl was used and the gas plating being carried out onsteel strip as in Example IV. In this 'case an alloy coating ofmagnesium and aluminum is." plated onto the steel strip, the temperaturebeing raised to bringabout disassociation of themixture oforganometallic compounds and deposition of the metal constituent.EXAMPLE VIII Copper plate is cleaned and heated in an atmosphere ofhelium at a temperature of about 385 C. and in which is introducedapproximately 10% of aluminum trimethyl. This compound boils at about135 C. and is caused to disassociate to deposit the metal.

EXAMPLE Ix One mol of aluminum alcoholate and 0.1 mol of chlorine isheated to approximately 400-500 C. to bring about disassociation of thealcoholate and drive off the alcohol under vacuum of 18-20 Hg. Thechlorine is used as a catalyst to assist the operation. Iodine r brominemay be substituted for chlorine where desired, and the temperatureincreased as necessary to bring about disassociation of the metalalcoholate and release of type.

Other organo-metallic compounds which may be used to gas plate magnesiumor aluminum as described are magnesium dimethyl; aluminum trimethyl;triarylmethylmagnesium halides; diphcnylethynylmagnesium, aluminumhydride magnesium and aluminum nitrides and such as will decompose undertemperature, pressure and inert atmosphere conditions imposed. The lightmetal halide compounds such as bromides, iodides or chlorides may beobtained from sea water or formed as by-products during the recovery orprocess of making various chemical compounds and products utilizingbrine-containing waters.

Coatings of these light metals may be of various thickness as desireddepending upon the use to which the article is to be put. A coating of0.001 to 0.0025 inch is adequate for providing protection againstcorrosion in most instances.

The process makes possible continuous straightline production ofcomposite magnesium-aluminum products, such as wire, cable, metal plate,strip, sheet material or screen. The thickness of the coating may becontrolled by limiting the duration of the gas plating or time thearticle remains in the plating enclosure. The invention is particularlyuseful in aluminizing metals where it is desirous that the metal bedeposited into the pores and interstices of the base metal surface toform a substantially integral outer shell of aluminum metal. Aluminummetal thus deposited on steel, for example, provides a corrosionresistant product.

The material being gas plated with the light metals may be composed ofvarious metals or alloys and in the various shapes and forms described.To clean the metal preparatory to gas plating, use may be made ofconventional methods, such as washing or immersing the material inalkali or acid solutions, and rinsing the same with clear hot water andheating to 150 to 200 C. for sufficient time to drive off all moistureand produce a perfectly dry surface. Electro-chemical cleaning methascommonly used also may be employed if desired as well as mechanicalcleaning methods, eg. wire brushing and sandblasting.

Pre-heating and drying of the article prior to gas plating is preferablycarried out in an inert atmosphere such as nitrogen, helium or the liketo prevent oxidation. Thereafter the heated and completely dry metalsurface is subjected to gas plating. Y

By employing gas plating in accordance with this invention, it ispossible to envelope the material or article by a metal film or plate ofany desired thickness, and which consists of substantially pure metal. Aprotective film is thus provided which film or plating does not haveoccluded foreign matter such as undesirable metals, salts, anodeparticles, bubbles and the like, which are inevitably plated out on thecathode along with the desired metal during ordinary electroplatingmethods.

Gas plating on the contrary, avoids these difliculties with respect tothe impurities occluded by way of the electrolyte during electroplating,inasmuch as the gas plating works best, in most cases, in the absence ofmoisture or water vapor. Oxygen and oxidizable materials are alsoabsent. The plating deposited by such gas plating method has beenobserved to produce a metal deposit which penetrates into the pores andinterstices of the substrate metal but does not produce the undesirablebrittle alloy effects as observed when such plating is applied by wetprocesses or molten metal plating methods.

It is not known the exact reason for this, but it is believed that thesebeneficial efiects are accounted for by reason of the freedom of themetal deposit from irn-- purities, particularly metal impurities whichproduce the brittle alloy characteristic property. The metal deposit atthe interstices of the substratum by gas plating produces a tenaciousintermediate portion which remains ductile and tough so that the metalthus plated can be worked as desired. Any desired thickness of platingmay be deposited by gas plating, for example, so thin that the metalarea is actually transparent and when deposited on a transparentsubstratum, such as glass, produces a smoked glass. The metal platingmay also be increased so as to provide a coating thickness such as $1 to,6 if desired, or greater. I,

In the use of conduit, pipe and the like conveying corrosive material,it is desirable to coat or plate the interior of the pipe so that itwill resist corrosion. This may be done by gas plating so that the innerwall is resistant to corrosion. Metal plating done in .this' manner isvery superior to wet plating methods because it has been dilficult tobring about uniform plating on the interior of hollow objects,especially conduits. Furthermore, employing conventional wetelectroplating methods there is always a certain amount. even thoughminor, of entrapment of electrolyte. While this may be imperceptibleunder ideal conditions, there is generally enough im purities plated outwith the metal to ultimately cause deterioration of the plated article.Gas plating eliminates these difiiculties because no electrolvte ispresent or required in order to carry out the process and as is aprerequisite element in performing the wet electrolytic plat mg process.

Further, gas plating makes it possible to bring nascent pure metal indirect contact with chemically clean substrate surfaces on which themetal is to be plated, and due to the deposition of the metal from agaseous state, the penetration of the same deeply into the pores andinterstices of the metal is accomplished without the inclusion ofimpurities and such as will alter the physical characteristics of themetal so that the interstitial plate portions function to actuallyenhance the physical characteristics of the base metal or substrate.

What is claimed is:

1. A method of gas plating light metal selected from the groupconsisting of aluminum and magnesium on the surface of an article, whichcomprises heating said article in an inert atmosphere, and contactingsaid heated article "with 1' gaseous heat-decomposable compound selectedfrom the groupconsisting of alkyl and aryl compounds of fsaid lightmetals, said article being heated to a temperature to cause thermaldecompoit'ion of said compound and deposition of the light metalconstituent onto the surface of the article whereby the same is coatedwith said light metal.

2. A product made in accordance with the method of claim .1.

.8 References Cited in the file of thl; patent UNITED STATES PATENTSWeber ..Y June 10, 1924 Marden et al June 26, 1928 Copper a Oct. 22,1929 r Loewe Apr. 19, 1938 Fischer June 30,.1953 Fink et al. Oct. 20,1953

1. A METHOD OF GAS PLATING LIGHT METAL SELECTED FROM THE GROUPCONSISTING OF ALUMINUM AND MAGNESIUM ON THE SURFACE OF AN ARTICLE, WHICHCOMPRISES HEATING SAID ARTICLE IN AN INERT ATMOSPHERE, AND CONTACTINGSAID HEATED ARTICLE WITH A GASEOUS HEAT-DECOMPOSABLE COMPOUND SELECTEDFROM THE GROUP CONSISTING OF ALKYL AND ARYL COMPOUNDS OF SAID LIGHTMETALS, SAID ARTICLE BEING HEATED TO A TEMPERATURE TO CAUSE THERMALDECOMPOSITION OF SAID COMPOUND AND DEPOSITION OF THE LIGHT METALCONSTITUENT ONTO THE SURFACE OF THE ARTICLE WHEREBY THE SAME IS COATEDWITH SAID LIGHT METAL.